In the prior art, it is known to provide multi-speed bicycles with both front and rear derailleurs which are used to selectively move the drive chain of the bicycle between the sprockets of the front and rear sprocket clusters of the bicycle. These front and rear derailleurs are mechanically actuated via respective ones of a pair of cables which extend between the derailleurs and a pair of shifter handles which are typically located on the bicycle frame so as to be easily accessible by the rider.
There is also known in the prior art single and multi-speed bicycles which include a shock absorbing front fork alone or in combination with a shock absorbing rear assembly. Shock absorbing front forks as currently known in the prior art typically comprise a pair of fluid-damped or spring-damped legs or pistons, the distal ends of which are attached to respective ends of the axle of the front wheel. Shock absorbing rear assemblies known in the prior art are provided in numerous configurations, and typically include a shock absorber which is extended between pairs of components which define the "rear triangle" of the bicycle frame, e.g., the seat tube, swingarms, chain stays, etc.
In view of various shortcomings associated with the traditional front and rear derailleurs which are actuated through the use of cables, there has been developed a shifting system for use in multi-speed bicycles wherein the front and rear derailleurs are configured to be actuated through the use of pressurized air instead of cables. This new air powered shifting system, wherein air lines are fluidly connected to the front and rear derailleurs as an alternative to cables, allows for very quick and virtually friction free gear changes as compared to the use of cables in the traditional cable actuated shifting system. As will be recognized, the new air powered shifting system currently requires that the bicycle be provided with an onboard pressurized air canister. This canister is attached to the bicycle frame (typically the down tube), and is capable of providing approximately three thousand shifts of the front and rear derailleurs prior to having to be repressurized or recharged. The recharging process is typically facilitated by pressurizing the canister at a gas station with a standard air compressor and tire inflation fittings.
Though this new air powered shifting system provides advantages over the traditional cable actuated shifting system, it also possesses certain deficiencies which detract from its overall utility. More particularly, since the canister of such air powered shifting system can only accommodate a prescribed volume of pressurized air, it has the capability of providing only a fixed amount of shifts before requiring a recharge. Though, as indicated above, the canister of the current air powered shifting system provides the capacity for approximately three thousand shifts of the front and rear derailleurs, the exhausting of the pressurized air supply when the rider of the bicycle is at a location far removed from a gas station or other source of pressurized air effectively precludes the rider from being able to shift the gearing on the bicycle.
The present invention addresses this shortcoming in the air powered shifting system by providing a shock absorbing bicycle frame having the capability of continuously recharging a pressure reservoir which itself serves as a pressurized air source for an air powered front and/or rear derailleur shifting system. In the present invention, a modified version of an existing shock absorbing front fork is employed in the bicycle frame to provide both the shock absorbing qualities of a standard shock absorbing front fork as well as a source or supply of pressurized air for the air powered shifting system. In particular, one leg or piston of the front fork is used to provide the standard shock absorbing quality of a shock absorbing front fork, with the other leg or piston serving as a "pump" to supply pressurized air to a pressure reservoir which is in turn fluidly connected to the air powered shifting system. The constant up and down motion of the front fork during normal riding of the bicycle provides the mechanical pumping action needed for the pump leg or piston to charge or pressurize the pressure reservoir. An air line fluidly connected to the top of the pump leg runs either externally or internally to the pressure reservoir which may comprise an air storage container or canister carried on the bicycle frame or disposed therein as a separate component, or may be formed as an integral portion of the bicycle frame itself. The supply of pressurized air could also be provided by the shock absorber of the rear assembly as an alternative to outfitting the bicycle with the modified shock absorbing front fork.